The long-term goal of this project is to elucidate how point mutations in genes encoding mitochondrial respiratory chain components cause human disease, particularly those involving neurological abnormalities. Defects in mitochondrial function are now being associated with an increasing number of disorders including Parkinson's disease. Thus, the mitochondrial diseases constitute an important area for research. The main focus during the next period of support will be upon a collaborative, multidisciplinary analysis of Leber's Hereditary Optic Neuropathy (LHON), a significant cause of inherited blindness. This approach will combine molecular genetics and biology, biochemistry and molecular genetics and biology, biochemistry and molecular enzymology, and somatic cell genetics. 1) The mitochondrial gene mutations causing LHON will be determined in a number of different families, some of which express severe neurological abnormalities in addition to the optic neuropathy. The available data indicate that the proximal cause of the disease is a mutation in one of the mitochondrial genes encoding complex I subunits. Mutations in the ND1 gene have been identified in two LHON families. 2) These genetic studies will be integrated with biochemical and biophysical studies of complex I (NADH - ubiquinone oxidoreductase) to further define the enzymological basis of LHON. 3) Defects in complex I are found in many mitochondrial diseases. A mutational analysis of the ND1 subunit will be undertaken using Paracoccus denitrificans as a bacterial genetic model system. Other examples of mitochondrial diseases will be analyzed using a similar multidisciplinary approach.